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Cobimetinib Side Effects

Medically reviewed by Last updated on Mar 21, 2022.


Commonly reported side effects of cobimetinib include: skin photosensitivity. Other side effects include: increased creatine phosphokinase in blood specimen. See below for a comprehensive list of adverse effects.

For the Consumer

Applies to cobimetinib: oral tablet

Side effects requiring immediate medical attention

Along with its needed effects, cobimetinib may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking cobimetinib:

More common

  • Abdominal or stomach pain or tenderness
  • bleeding gums
  • blurred vision or any other change in vision
  • chest discomfort or pain
  • chills
  • clay colored stools
  • coughing up blood
  • dark urine
  • decreased appetite
  • difficulty in breathing or swallowing
  • dizziness
  • faintness
  • fast irregular or pounding heartbeat
  • fever
  • headache
  • increased menstrual flow or vaginal bleeding
  • increased sensitivity of the skin to sunlight
  • itching or skin rash
  • loss of appetite
  • muscle cramps or spasms
  • muscle pain or stiffness
  • nausea and vomiting
  • nervousness
  • nosebleeds
  • paralysis
  • pounding in the ears
  • prolonged bleeding from cuts
  • red or black, tarry stools
  • red or dark brown urine
  • redness or other discoloration of the skin
  • seeing flashes or sparks of light
  • seeing floating spots before the eyes, or a veil or curtain appearing across part of vision
  • severe sunburn
  • slow or fast heartbeat
  • swelling of the feet or lower legs
  • unusual tiredness or weakness
  • yellow eyes or skin

Side effects not requiring immediate medical attention

Some side effects of cobimetinib may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

For Healthcare Professionals

Applies to cobimetinib: oral tablet


The most commonly reported adverse reactions (more than 35%) were increased creatinine, increased CPK, lymphopenia, increased AST, increased alkaline phosphatase, increased ALT, hypophosphatemia, anemia, increased gamma-glutamyltransferase, diarrhea, photosensitivity reactions, hypoalbuminemia, nausea, and hyponatremia.[Ref]


Very common (10% or more): Increased creatinine (99.6%) Common (1% to 10%)[Ref]


Very common (10% or more): Increased CPK (79%)[Ref]


Very common (10% or more): Increased AST (73%), increased alkaline phosphatase (71%), increased ALT (68%), increased gamma-glutamyltransferase (65%)

Frequency not reported: Increased total bilirubin[Ref]


Very common (10% or more): Lymphopenia (73%), anemia (69%), thrombocytopenia (18%), hemorrhage (e.g., rectal, hemorrhoidal, GI tract, uterine, vaginal, pulmonary, cerebral, subarachnoid, ocular, eye, conjunctival, retinal, reproductive system, melena, hematemesis, hematochezia, gingival bleeding, metrorrhagia, hemorrhagic ovarian cyst, menometrorrhagia, menorrhagia, hemoptysis, subgaleal hematoma, hematuria, epistaxis, contusion, traumatic hematoma, ecchymosis, purpura, nail bed bleeding)[Ref]


Very common (10% or more): Dehydration, hypophosphatemia (68%), hypoalbuminemia (42%), hyponatremia (38%), hyperkalemia (26%), hypokalemia (25%), hypocalcemia (24%)[Ref]


Very common (10% or more): Diarrhea (60%), nausea (41%), vomiting (24%), stomatitis (14%)[Ref]


Very common (10% or more): Photosensitivity reactions (46%), acneiform dermatitis (16%), alopecia (15%), hyperkeratosis (11%), erythema (10%), maculopapular rash, dermatitis acneiform rash[Ref]


Very common (10% or more): Pyrexia (28%), hemorrhage (13%), chills (10%) Common (1% to 10%):[Ref]


Very common (10% or more): Decreased LVEF (26%), hypertension (15%)[Ref]


Very common (10% or more): Vision impaired (e.g., vision blurred, visual acuity reduced, visual impairment) (15%), chorioretinopathy (e.g., retinal detachment, detachment of retinal pigment epithelium, detachment of macular retinal pigment epithelium) (13%), retinal detachment (e.g., retinal detachment, detachment of retinal pigment epithelium, detachment of macular retinal pigment epithelium) (12%)

Common (1% to 10%): Serious retinopathy (chorioretinopathy, retinal detachment)

Frequency not reported: Retinal vein occlusion[Ref]


Common (1% to 10%): Cutaneous squamous cell carcinoma/keratoacanthoma, basal cell carcinoma

Uncommon (0.1% to 1%): Second primary melanoma, non-cutaneous malignancies[Ref]


1. "Product Information. Cotellic (cobimetinib)." Genentech (2015):

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.